The objective of Evolved UTRA and UTRAN is to develop a radio access network towards a high-data-rate, low-latency, packet-optimized system with improved system capacity and coverage. In order to achieve this, an evolution of the radio interface as well as the radio network architecture should be considered. For example, instead of using CDMA which is currently used in 3GPP, OFDMA and FDMA are proposed air interface technologies to be used in the downlink and uplink transmissions, respectively. For example, one big change is to apply all packet switched services in LTE, which means all the voice calls will be made on a packet switched basis.
FIG. 1 illustrates a conventional packet-optimized radio access network, in this case a UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN has one or more radio network controllers (RNCs) 104 and base stations 102, referred to as Node-Bs or evolved Node-Bs (eNBs) by 3GPP, which collectively provide for the geographic coverage for wireless communications with WTRUs 100, referred to as user equipments (UEs) by 3 GPP. The geographic coverage area of a Node-B 102 is referred to as a cell. The UTRAN is connected to a core network (CN) 106.
In UMTS, the initial power determined for PRACH message (after initial RACH access preamble) is based on following equation:Pmessage-control=Ppreamble+Power offset Pp-m;  Equation (1)where Ppreamble is the power of the last transmitted preamble, Pp-m (in dB) is the signaled power offset between the last transmitted preamble and the control part of the message.
For uplink dedicated physical control channel (DPCCH), the power of the first DPCCH transmission is established as follows:DPCCH_Initial_power=DPCCH_Power_offset—CPICH_RSCP;  Equation (2)where DPCCH_Power_offset is signaled having the value of IE “DPCCH Power offset” in IE “Uplink DPCH power control info”; and CPICH_RSCP is the received signal code power of the CPICH measured by the wireless transmit receive unit (WTRU).
For Evolved UTRA the uplink (UL) power control is handed in a different manner. The setting of the WTRU Transmit Power Ppusch for the physical uplink shared channel (PUSCH transmissions are defined by:Ppusch=min(Pmax,10 log10(M)+Po+α·PL+Δmcs+f(Δi));  Equation (3)where:                Pmax is the maximum allowed power that depends on the UE power class;        M is the number of assigned resource blocks as indicated in the UL scheduling grant;        Po is a UE specific parameter with 1 dB resolution;        α is cell specific path loss compensation factor (can be set to one to allow full path loss compensation) that has 8 values from 0.4 to 1 in steps of 0.1 with one of the possible values being zero;        PL is the downlink pathloss calculated in the UE from a RSRP measurement and signaled RS transmit power;        Δmcs is signaled by RRC (Δmcs table entries can be set to zero);                    MCS signaled in each UL scheduling grant; and                        Δi is a UE specific correction value and is defined differently dependent on scheduling as given by:                    Scheduled                            Δi is included in each UL scheduling grant;                Function ƒ(*) signaled via higher layers; and                ƒ(*) represents either accumulation or current absolute value;                                    Not scheduled                            Δi is included in each DL scheduling assignment or jointly coded with other UE specific correction values on a TPC PDCCH;                The UE attempts to detect a TPC PDCCH and a DL scheduling frame on every subframe except when in DRX;                The Δi from a downlink (DL) scheduling assignment overrides any command from a TPC PDCCH when both are received in a given subframe; and                Function ƒ(*) represents accumulation only.                                                
The setting of the UE Transmit power Ppucch for the physical uplink control channel (PUCCH) transmissions is defined by:Ppucch=min(Pmax,10 log10(Mpucch)+Po—pucch+PL+Δmcs—pucch+g(Δj))  Equation (4)where:                Mpucch is the number of assigned resource blocks for the PUCCH;        Δmcs—pucch is signaled by RRC (Δmcs—pucch table entries can be set to zero);                    MCS is signaled using higher layer signaling;                        Po—pucch is a UE specific parameter with 1 dB resolution; and        Δj is a UE specific correction value, also referred to as a TPC command, included in a DL scheduling assignment or sent jointly coded with other UE specific correction values on a TPC PDCCH;                    The UE attempts to detect a TPC PDCCH and a DL scheduling frame on every subframe except when in DRX;            The TPC command from a DL scheduling assignment overrides any command from a TPC PDCCH when both are received in a given subframe; and            Function g(*) represents accumulation.The power control parameters are signaled to the UE prior to transmission in the grant message sent by the eNB, except for the PL parameter which is measured at the UE.                        
For both UMTS cases, the initial power level is not determined and signaled by the eNB. Instead, the power level is determined by the UE based on the power offset value and either previous transmission power (for RACH message) or measured signal strength (for DPCCH). This allows the UE to set its initial power to an acceptable level. However, in the case of Enhance UTRA, the power control is signaled by the eNB to the UE and the eNB has no knowledge as to the power transmitted by the UE in its RACH signal. Therefore, improved controls or signaling needs to be added to the power control so that the UE can transmit at the correct power after the initial RACH process.